This invention relates to a coin sorter for use in a vending machine or the like and, more particularly, to a coin sorter having a bridge circuit for examining the genuineness and kinds of coins inserted in the sorter.
One type of known coin sorter for use in a vending machine has a coin detecting coil that is disposed along a passage through which inserted coins roll on. The detecting coil is connected to one arm of a bridge circuit and fed with an AC voltage. An example of such prior art coin sorter is shown in FIG. 1.
Referring to FIG. 1, an AC bridge circuit 1 has arms which comprise a coin detecting coil SC, fixed resistors R.sub.10 and R.sub.11, and a variable resistor R.sub.12 plus a variable coil L.sub.11, respectively. The coil SC includes an induction coil, to which an oscillator O applies an AC voltage of a constant frequency, so that the coil develops an alternating magnetic field. The detecting coil is shown consisting of an equivalent reactance L.sub.0 and an equivalent resistance R.sub.0. A semi-bridge circuit 2 consisting of a fixed resistor R.sub.21, a variable resistor R.sub.22 and a variable coil L.sub.21 is connected in parallel with the bridge circuit 1. Another semi-bridge circuit 3 consisting of a fixed resistor R.sub.31, a variable resistor R.sub.32 and a variable coil L.sub.31 is also connected in parallel with the circuit 1. Since the variable resistors R.sub.12, R.sub.22, R.sub.32 of the the circuits 1, 2, 3 and the reactances of the variable coils L.sub.11, L.sub.21, L.sub.31 are adjusted so as to have different values, the system shown is capable of separating coins into three different types. The output terminals of the bridge circuits 1, 2, 3 are connected to differential amplifiers 4, 5 and 6, respectively, and the outputs of these amplifiers are connected with the comparison inputs of comparators 10, 11 and 12, respectively, via rectifier circuits 7, 8 and 9, respectively.
As known in the prior art, the bridge circuit is set such that it changes from balanced state to unbalanced state once because of a change in the reactance of the coin detecting coil SC which takes place when an acceptable coin passes the coil SC. In particular, the voltages at the terminals A, B, C and D of the bridge circuit 1 vary depending on the presence or absence of a coin as shown in the vector diagram of FIG. 2.
When a predetermined voltage V.sub.0 is applied between the terminals A and B of the circuit 1 in standby state where the system is ready for insertion of a coin, the potential at point D, between the equivalent reactance L.sub.0 and the equivalent resistance R.sub.0 of the coil SC, and the potential at the terminal C, between the resistance R.sub.0 and fixed resistor R.sub.10, are shown at points D and C, respectively, of FIG. 2, because reactance leads resistance by a phase angle of 90.degree.. In this case, the potentials at terminals E.sub.1, E.sub.2 and E.sub.3 of the respective circuits 1, 2 and 3 have unbalanced relation to the potential at the terminal C, and therefore the differential amplifiers 4, 5 and 6 each deliver a large unbalanced voltage.
When a coin of a first kind, for example, a five cent coin, is placed at the position of the detecting coin SC, the reactance of the coil SC changes in response to the coin, thus shifting the potentials at the terminal C and the point D to C.sub.01 and D.sub.01, respectively. In case where a coin of a second kind such as a ten cent coin is put at the position of the coil SC, the reactance of the coil SC changes to a value different from that of the previous case of a five cent coin because of differences in coin characteristics including material, diameter and thickness. The result is that the potentials at the terminal C and the point D are moved to C.sub.02 and D.sub.02, respectively. When a coin of a third kind, for example, a twenty-five cent coin, is located at the position of the coil SC, the reactance of the coil SC varies according to the characteristics of the coin including material, diameter and thickness, so that the potentials at the terminal C and the point D are brought to C.sub.03 and D.sub. 03, respectively.
As the reactance of the coil SC undergoes a change according to the characteristics of a coin in this manner, the variable resistor R.sub.11, R.sub.21, R.sub.31 and the variable coils L.sub.11, L.sub.21, L.sub.31 of the bridge circuits 1, 2, 3 are individually adjusted so that when a five cent coin passes the coil SC, the potential at the terminal C is balanced once by the potential at the terminal E.sub.1 of the bridge circuit 1, when a ten cent coin moves past the coil SC, the potential at the terminal C is balanced once by the potential at the terminal E.sub.2 of the circuit 2, and when a twenty-five cent coin passes the coil SC, the potential at the terminal C is balanced once by the potential at the terminal E.sub.3 of the circuit 3, for example. Therefore, when the bridge circuits 1, 2 and 3 are balanced, the outputs of the amplifiers 4, 5 and 6 or the rectifiers 7, 8 and 9 become zero, which is utilized to examine the genuineness of each coin introduced. For this purpose, when the comparison input signals to the comparator circuits 10, 11 and 12 do not reach reference values COM.sub.1, COM.sub.2 and COM.sub.3, respectively, their respective comparator circuits deliver a single pulse.
Although such a coin sorter in a conventional apparatus is able to examine the genuineness of each coin and denominations of accepted coins by the simple configuration making use of the balance state of each bridge circuit, it requires a differential amplifier, a rectifier and a comparator circuit for each kind of coin to be detected, thus necessitating a number of expensive analog circuits. Such circuits have many circuit components and are expensive to manufacture.